1. Field of the Invention
The present invention relates to a glazing for a vehicle--and more particularly for a motor vehicle--having improved acoustic insulation performances, and especially in relation to noises of aerodynamic origin.
2. Discussion of the Background
Of all the qualities contributing to comfort in modern transportation vehicles such as trains and automobiles, silence has become decisive. Actually, other sources of annoyance such as of mechanical, heat, or visibility origin, etc. have been gradually overcome. But the improvement of acoustical comfort presents new difficulties as the noises themselves, such as engine noises, and driving or suspension noises, have already been treated at their origin or during their propagation, either by air (absorbing coatings in particular) or by solids (elastomer connecting parts, for example). The aerodynamic noises created by the friction of air moving over the vehicle have been able, at least in part, to be treated at their source, i.e., to save energy, shapes have been changed, penetration in the air has been improved and turbulences which are themselves sources of aerodynamic noise have been reduced.
However, both in the design of the cars of rapid modern trains and in that of automobiles, what could be done to treat the sources of aerodynamic noises has been done and reducing what noises remain, whether the noises are those of a perfect laminar flow or the reduction of the turbulences, requires disproportionate measures whose cost would be incompatible with the profitability of the design studied.
Of the walls of the vehicle that separate the source of outside aerodynamic noise from the interior space where the passenger is located, the glazings are the most difficult to treat. Fibrous or pasty absorbent materials reserved for opaque walls cannot be used and for practical or weight reasons, thicknesses cannot be thoughtlessly increased.